1. Field of the Invention
The present invention relates to a keyboard arrangement and more particularly relates to a keyboard arrangement of the alpha-numeric type as frequently utilized in connection with computers, word processors and the like. However, it is to be appreciated that the invention is not restricted to use in such circumstances and may find other applications.
2. Discussion of the Prior Art
FIG. 1 is a diagrammatic view of part of a conventional electronic alpha-numeric keyboard.
Although the keys on the keyboard may be provided in staggered rows, or in some other array, topologically the keys may be considered to constitute a regular array of rows and columns. In the presently described typical keyboard a transverse conductor, such as the conductor 1 or 2 is associated with each row of keys, and a vertical conductor, such as the conductors 3 and 4 are associated with each column of keys. Whenever a key is depressed the key serves to connect electrically the conductor associated with the row of keys in which the key is situated with the conductor associated with the column in which the key is situated. Thus, for example, if the key 5 is pressed the conductor 2 is electrically connected to the conductor 4.
Only part of the conventional keyboard is illustrated in FIG. 1, sufficient to illustrate the arrangement.
In order to determine which key has been pressed at any instant a microprocessor 6 is provided which controls a row interrogator 7. The row interrogator 7 supplies sequential pulses, such as the pulses 9 to respective conductors associated with the rows of keys. Thus, for example, the conductor 1 will receive an initial pulse during a cycle of operation, and the conductor 2 will receive a subsequent, later pulse. Further pulses are applied in turn, after appropriate brief time delays, to each of the conductors associated with the respective rows of keys. A diode may be integrated in each key to allow any number of keys to be depressed and still be properly detected.
At any instant only one key is depressed, and thus one conductor associated with a row of keys is connected to one conductor associated with a column of keys. As mentioned if the key 5 is depressed the conductor 2 is connected to the conductor 4. Thus, when the pulse 9 from the row interrogator is fed to the key 5 an output pulse is provided on the conductor 4. Each of the conductors 3,4 etc. associated with a column of keys is associated with a respective column latch 10. When such a latch receives a pulse the latch enters a latched state. A column latch interrogator 11 is provided which, after each pulse 9 has been supplied from the row interrogator, interrogates the column latches 10 to ascertain if a column latch has been latched by receipt of a pulse. The column latch interrogator is controlled by the microprocessor, and resets the latches it interrogates. When the column latch interrogator determines that a latch 10 has been latched, the appropriate information is relayed to the microprocessor, and the microprocessor can then act upon the information provided to generate a signal representative of the particular key that was depressed during the interrogation sequence. The interrogation sequence can then repeat.
One problem that can be experienced with an arrangement as described is that as the microprocessor interrogates the rows, with the row interrogator as described, electro-magnetic radiation is emitted by the keyboard corresponding to the pulses supplied to the rows. The nature of this emitted radiation varies when a row is interrogated which has a key depressed. Also the nature of the emitted radiation is such that the radiation differs depending upon precisely which key in the row is depressed.
Consequently, it is possible for a person provided with appropriate "eavesdropping" equipment to detect the radiation emitted by the keyboard, and by processing that detected radiation appropriately, to determine which keys have been pressed, and in which order. Thus, effectively, an appropriate "eavesdropping" device can effectively read the information that is entered through the keyboard.